Internet Protocol (IP)-based communication networks have not reduced demands for clock synchronization. On the contrary, for demands of cost, safety, and services, the IP clock synchronization becomes more and more important. Among the various existing IP clock technologies, such as circuit emulation services over packet switched (CESoP), timing over packet (ToP), network time protocol (NTP), the ToP technology is a relatively new technology. For the IP clock technology, the Institute for Electrical and Electronics Engineers (IEEE) also introduced an IEEE 1588 precision time protocol (PTP) standard. The IEEE 1588 PTP not only inherits the characteristics of performing frequency synchronization on master and slave clocks in the technology above, but also implements time synchronization, that is, phase synchronization.
However, in the IEEE 1588 PTP, it is necessary to collect all time stamps transmitted between the master clock and the slave clock. The time stamps are stamped by the time stamp engines located at the master clock side and the slave clock side. The time stamps mainly include transmitting time and receiving time of information such as a synchronous packet (Sync packet), follow up information (Follow_Up information), delay request (Delay_Req) packet, and a delay response (Delay_Resp) packet. The frequency synchronization adjustment and time synchronization adjustment of the master clock and the slave clock can be performed only after collecting sufficient information of time stamps between the master clock and the slave clock.
In the process of implementing the present invention, the inventor finds that there are at least the following disadvantages in the conventional art. Too much link bandwidth resources are occupied in the aforesaid process. Especially, when the network transmission conditions are deteriorated and the frequency of transmitting packets needs to be increased for frequency synchronization, such a disadvantage that the clock synchronization occupies too much link bandwidth resources becomes more apparent. In addition, when only one time stamp engine exists at the slave clock side, the time of stamping a time stamp at a local position of the slave clock has to be different from the time of the local frequency synchronization; otherwise, due to the local frequency adjustment, the value of the local time stamp is influenced. Therefore, correct calculation is not able to be performed according to the obtained time stamps, and the frequency synchronization/time synchronization is thus influenced.